\chapter{Galactic Chemical Evolution and Estimation of FUN CAIs Formation}
\label{chap:gce}

Galactic Chemical Evolution (GCE) is the study of the evolution of gas into
stars and of the chemical composition of a galaxy. ref
Various of species are generated during stellar evolution. Some of them
will be locked in low mass stars which evolves slowly or in compact objects 
which are left behind stellar explosive events. Some of them will be 
ejected into the interstellar medium (ISM) and become the ingredients of
the next generation of stars. The newer generation of stars then have some
heavier species like carbon and oxygen to start with, which are not present
in the first generation of stars. These so called primary species will 
alter the evolution path of stars and help produce secondary species, which
can only be synthesized when some certain primary species are present.
Both primary and secondary species will travel around the galaxy and get 
together with others to collapse to form new stars. So the chemical
composition of stars depends on how the species travel and what chemical
form they are in. Studying the chemical composition of current and early
solar system will help us understand the chemical evolution history of
the galaxy.

Different kind of models of GCE can be developed, simple or sophisticated.
Generally a GCE model requires stellar properties and yield, stellar 
initial mass function (IMF), star formation rate (SFR) and gaseous flows.
Our study of the dense type Ia supernovae in chapter ref
would contribute to the yield part of GCE. We also explored dust formation
in chapter ref and equilibrium chemical form in chapter ref.
The detailed GCE model would be a much larger project than a single PhD
thesis work. However we can try some rough estimation of the CAIs
formation with heterogeneous neutron-rich iron-group isotope inputs
due to the rareness of dense type Ia supernovae.
